Purified Precipitated Calcium Carbonate and Purified Calcium Silicate Compounds, a Method for Their Production, and Their Use as Paper Fillers

ABSTRACT

Methods for the production of high purity calcium carbonate and high purity calcium silicate. Products are washed before introduction into a paper machine furnish, to avoid filler loss and brightness reversion. In one embodiment, multiple superatmospheric reactors may be provided, for switching production between reactors, and advantageously utilizing process waste heat. On site production of both precipitated calcium carbonate and calcium silicate hydrates is thus achieved in a paper mill.

RELATED PATENT APPLICATIONS

This application claims priority from and is a Continuation-In-Part of prior allowed U.S. patent application Ser. No. 09/797,173, filed Feb. 28, 2001, which issued as U.S. Pat. No. 7,048,900 on May 23, 2006, entitled “METHOD AND APPARATUS FOR PRODUCTION OF PRECIPITATED CALCIUM CARBONATE AND SILICATE COMPOUNDS IN COMMON PROCESS EQUIPMENT” which claimed priority from prior U.S. Provisional Patent Application Ser. No. 60/265,657, filed on Jan. 31, 2001, and the disclosures of each of the above identified applications and patents are incorporated herein in their entirety by this reference, including their specification, drawing figures, and claims.

COPYRIGHT RIGHTS IN THE DRAWING

A portion of the disclosure of this patent document contains material that is subject to copyright protection. The applicant no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

TECHNICAL FIELD

This disclosure is with respect to improved precipitated calcium carbonate compositions, to improved calcium silicate hydrate compositions, as well as to methods for their manufacture, and to methods for their use as paper fillers.

BACKGROUND

The new “internet” economy has created a need for better appearing and for higher performance papers. Desirable aesthetic qualities require papers to be brighter, more opaque, and to have a smoother printing surface. Better qualities of these properties are useful to accommodate increasingly important uses of papers, such as ink jet printing and desktop publishing. And, higher performance requirements are sought in industrial papers like paper board and packaging (used to ship items ordered via the internet) which paper types require components with very high mechanical strength. At the same time, escalating shipping and postal costs mean that users would also benefit from lighter weight papers. In other words, it would be desirable to provide industrial paper with higher mechanical strength, higher brightness, higher opacity, yet still having improved printability, weigh less, and made at a lower basis weight. With paper fillers and paper manufacturing techniques known or practiced heretofore, the juxtaposition of these requirements has not been feasible.

Presently, the paper industry adds filler to paper in order to improve some of the key performance attributes. However, nearly all of the paper fillers currently available have some drawbacks associated with their use. For example, the best known filler for improving the optical properties of paper is titanium dioxide (TiO₂). Although it can be used to dramatically improve the optical properties of paper, unfortunately, TiO₂ has some major disadvantages. First, it is very expensive, on the order of about US$2,000 per ton at time of filing of this patent application. Second, it is highly abrasive to processing machinery. Third, it is usually shipped in a slurry form, which requires dispersant additives to prevent settling; that both adds cost and creates paper machine runnability issues. Finally, TiO₂ must be produced off-site, remotely from the paper mill, shipped to customers, thus adding a large transportation cost.

Other fillers, like silica and calcium silicate, are sometimes used to improve sheet bulk, print quality, and other paper properties. Here again, one of the major disadvantages to these products is that they reduce sheet strength and are expensive (silica at about US$3,000 to about US$4,000 per ton, and calcium silicate at about US$800 to about US$1,000 per ton at time of filing this patent application). These products, like TiO₂, are also typically produced off-site, and carry a large transportation cost.

In an effort to reduce production costs, the industry is increasingly switching to commodity fillers such as ground or precipitated calcium carbonate. Precipitated calcium carbonate is perhaps best suited for improving the optical and print qualities of paper. It can also be produced on-site (at a paper mill), thus reducing or eliminating transportation costs. Unfortunately, calcium carbonate is not as effective as TiO₂ or silica based fillers. Moreover, it significantly reduces the strength performance of paper, in addition to causing undesirable dusting.

Importantly, it must also be appreciated that the conventional process for the manufacture of PCC also has several limitations. First, the reaction takes place at atmospheric pressure in an “open” vessel, using a batch process technique. Such processes also require a high CO₂ concentration (15%-20% by volume) in a combustion gas waste stream, and require a long reaction time (often from about 180 to about 200 minutes) to achieve the formation of the desired carbonate species. Conventional PCC manufacturing also requires large size reactors, (about 200 USgal/ton/day of PCC capacity). Additionally, a large building is required to house such PCC reactors, and consequently, a large sized site is a requirement for such a reactor building. Resultantly, capital for the building, equipment, and construction is significant.

In view of the above, there is a definite and as yet unmet need in the paper industry for a high performance specialty filler manufacturing process, especially for such a process that can produce important commodity fillers like PCC. Moreover, it would be desirable for such a high performance process to be technologically superior, i.e., produce better quality filler products at lower costs than are presently available.

Also, it would be desirable to find a new, high performance specialty filler that would, among other things, improve the aesthetic properties of paper (brightness, opacity, smoothness, print quality, etc.) as well as, and at the same time, and the mechanical properties of paper, (bulk, stiffness, etc.), without decreasing any strength properties. Even more desirably, such a filler would be available for supply as a slurry that is free of dispersant. Finally, it would be desirable that such a high performance filler be available from an on-site production facility, in order to eliminate transportation costs for the finished filler.

With regard to the production of precipitated calcium carbonate, it would also be desirable to provide improvements over conventional batch process so as to reduce or eliminate certain current limitations. For example, in an ideal situation, it would be desirable to produce precipitated calcium carbonate using very low concentration CO₂ (as low as about 5.0% CO₂ by volume, or less), while nonetheless significantly increasing the reaction rate, in order to reduce the size of reactors required from the current 200 gal/ton/day by at least half, and more preferably, by at least one fourth, i.e, to as low as about 50 gal/ton/day or less reactor size. Moreover, it would be desirable to reduce required building size, and thus reduce both process equipment costs and overall capital costs for such plants.

Also, it would be highly desirable to provide a method and apparatus that, with common capital equipment, is capable of both the production of the above mentioned high performance specialty filler as well as the production of precipitated calcium carbonate.

In many situations, it would be advantageous to provide fillers useful for producing both wood free papers (normally alkaline, manufactured at wet end pH>7.0), and wood containing papers (normally acidic, manufactured at wet end pH<7.0).

Further, it would often be advantageous to provide a method and apparatus, including equipment design, and process equipment configuration that produces both purified precipitated calcium carbonate and purified calcium silicate hydrates utilizing, at least in part, common process reactors.

Moreover, it would often be useful to provide an improved, purified precipitated calcium carbonate product that can be utilized in paper to improve brightness, opacity, and bulk.

Further, in many applications, it would be useful to provide an improved, purified multiphase calcium silicate hydrate that, when used in the manufacture of paper will:

-   -   Improve opacity over precipitated calcium carbonates;     -   Improve scattering power over precipitated calcium carbonates;     -   Improve brightness over precipitated calcium carbonates;     -   Improve sheet caliper over precipitated calcium carbonates;     -   Improve sheet bulk over precipitated calcium carbonates;     -   Improve sheet stiffness over precipitated calcium carbonates;     -   Improve sheet porosity over precipitated calcium carbonates;     -   Improve surface smoothness over precipitated calcium carbonates;     -   Improve sheet tensile over precipitated calcium carbonates;     -   Improve sheet formation over precipitated calcium carbonates;     -   Improve the intrinsic sheet water and oil absorption over         precipitated calcium carbonates;     -   Improve print quality over paper filled with precipitated         calcium carbonates;     -   Reduce print show through over paper filled with precipitated         calcium carbonates;

Finally, in spite of a myriad of prior art attempts at providing acid stable precipitated calcium carbonate compositions, there remain various paper manufacturing situations wherein a purified, acid resistant precipitated calcium carbonate composition would be advantageous in the manufacture of various paper grades.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be described by way of exemplary embodiments, some aspects of which are illustrated in the various accompanying drawing figures, in which like references denote similar elements, and in which:

FIG. 1 is a brightness reversion curve, illustrating the loss of brightness as pH is increased, with respect to a particular grade of paper manufactured with 25% Kraft pulp and 75% wood containing fiber.

FIG. 2 is graphical illustration of the stability over time of deionized water washed precipitated calcium carbonate, in the aragonite form, at various pH levels.

FIG. 3 is graphical illustration of the stability over time of deionized water washed precipitated calcium carbonate, in the scalenohedral form, at various pH levels.

FIG. 4 is graphical illustration of the stability over time of deionized water washed precipitated calcium carbonate, in the rhombohedral form, at various pH levels.

FIG. 5 is a graphical illustration of the stability over time at various pH levels, of deionized water washed precipitated calcium carbonate, in the aragonite form as manufactured using in-situ treatment using sodium polyacrylate and calcium chloride.

FIG. 6 is a graphical illustration of the short term stability over time at various pH levels, of a carbon dioxide treated calcium silicate hydrate nanofibre (“SNF”) composition.

FIG. 7 is a graphical illustration of the long term stability over time at various pH levels, of a carbon dioxide treated calcium silicate hydrate nanofibre (“SNF”) composition.

FIG. 8 is a graphical illustration of the short term stability over time at various pH levels, of a sulfuric acid treated calcium silicate hydrate nanofibre (“SNF”) composition.

FIG. 9 is a graphical illustration of the long term stability over time at various pH levels, of a sulfuric acid treated calcium silicate hydrate nanofibre (“SNF”) composition.

FIG. 10 is a graphical illustration of the short term stability over time at various pH levels, of an oxalic acid treated calcium silicate hydrate nanofibre (“SNF”) composition.

FIG. 11 is a graphical illustration of the long term stability over time at various pH levels, of an oxalic acid treated calcium silicate hydrate nanofibre (“SNF”) composition.

FIG. 12 is a graphical illustration of the short term stability over time at various pH levels, of an aluminum sulfate treated calcium silicate hydrate nanofibre (“SNF”) composition.

FIG. 13 is a graphical illustration of the long term stability over time at various pH levels, of an aluminum sulfate treated calcium silicate hydrate nanofibre (“SNF”) composition.

FIG. 14 is a graphical illustration of the short term stability over time at various pH levels, of a calcium silicate hydrate nanofibre (“SNF”) composition treated using a proprietary composition known as Colloid 211.

FIG. 15 is a graphical illustration of the long term stability over time at various pH levels, of a calcium silicate hydrate nanofibre (“SNF”) composition treated using a proprietary composition known as Colloid 211.

FIG. 16 is a graphical illustration of the short term stability over time at various pH levels, of a hexametaphosphate treated calcium silicate hydrate nanofibre (“SNF”) composition.

FIG. 17 is a graphical illustration of the long term stability over time at various pH levels, of a hexametaphosphate treated calcium silicate hydrate nanofibre (“SNF”) composition.

The foregoing figures, being merely exemplary, contain various elements that may be present or omitted from actual embodiments which may be implemented for a suitable composition for use as a paper filler, depending upon the circumstances. Further, similar aspects may be denoted with similar symbols, but utilizing a “prime” symbol as a suffix—“′”—and these shall be considered the functional equivalent of similar aspects or parts without such prime suffix symbols thereafter, as such nomenclatures is utilized in order to avoid unnecessary duplicate explanation of features or of the function thereof. An attempt has been made to illustrate in the figures at least those elements that are significant for an understanding of the various embodiments and aspects of the invention. However, various other aspects of a suitable fillers may be utilized in order to provide a reliable, functionally useful fillers that especially provide suitable bulk, opacity, and brightness, by providing novel, high purity filler material compositions suitable for application at various pH ranges.

DETAILED DESCRIPTION

Precipitated Calcium Carbonate (PCC)

Detailed Description of the Process Variables

The basic chemistry for producing calcium carbonates is well known, and the basic steps of calcination, slaking, and carbonation, were noted above. The following chemical reactions describe such basic steps:

The conventional industrial process for production of precipitated calcium carbonate is performed by providing a slurry of approximately 200 g/L of calcium hydroxide in an atmospheric pressure reactor, and then bubbling a gas stream containing carbon dioxide at about 15-20% by volume into the reactor. In commercially employed PCC production processes, reaction rates in the range of from about 0.5 grams per liter of calcium hydroxide per minute to about 1.5 grams per liter of calcium hydroxide per minute are commonly employed. Thus, in prior art PCC batch production processes, the time required to complete the carbonation reaction is from approximately 120 to approximately 240 minutes. That relatively slow overall reaction rate results in a requirement for large carbonation reactors (reactors in the 18,000 to 20,000 gallon range are common), with the associated high capital costs.

In my previous patent application, I disclosed a method for the high speed manufacturing of PCC is based on the ionic reactions involved in the manufacturing process as described below: Ca(OH)_(2 (slurry))→Ca⁺⁺+2OH⁻ SLOW(K_(eq)=6.46×10⁻⁶)  (4) CO_(2 (gas))+H₂O→H₂CO_(3 (aq)) FAST(K_(eq)=0.035)  (5) H₂CO_(3 (aq))+OH⁻→H₂O+HCO₃ ⁻ SLOW(K_(eq)=4.5×10⁻⁷)  (6) HCO₃ ⁻+OH⁻→H₂O+CO₃ ⁼ _((aq)) SLOW(K_(eq)=4.7×10⁻¹¹)  (7)

The dissolution of Ca(OH)₂ slurry into calcium ions is a slow process. The solubility of lime in water is inversely affected by the temperature of the slurry. For example, the solubility of pure CaO at 32° F. is 0.14% and at 212° F., it drops to 0.05%. The dissolution of CO₂ into water to give carbonic acid (equation 5) is fast, but the subsequent ionic reactions with hydroxyl ions to produce carbonate ions (CO₃ ⁼) are slow (equations 6 and 7). The formation of calcium carbonate takes place via the following ionic reaction:

In summary, the rate controlling unit operations in the manufacture of PCC are 1) mass transfer of CO₂ into water and 2) the dissolution of Ca⁺⁺ ion from the Ca(OH)₂ slurry.

In part, the present invention includes a process for increasing the rate of reaction by carrying out the carbonation reaction under pressure. This is accomplished in a specially designed reactor vessel, which can be operated under pressure. For the purpose of this invention, the following reaction variables, sequentially, are employed to set a desired rate of reaction, filler product morphology, shape, size, and optical properties (such as scattering power).

-   -   1) Reaction Pressure     -   2) Concentration of Carbon Dioxide     -   3) Rate of Flow of Carbon Dioxide     -   4) Concentration of Ca(OH)₂     -   5) Reaction Temperature     -   6) Rate of Agitation

The present invention involves carrying out the carbonation reaction between CO₂ and Ca(OH)₂ under pressure in a carbonation reactor which is a pressure vessel. This novel process involves bubbling CO₂ into the Ca(OH)₂ slurry in reactor where the pressure can range from above atmospheric pressure to as much as about 100 psig. Preferably, the pressure in the reactor is maintained at up to about 30 psig, and more preferably, the pressure in the reactor is maintained in the range from about 15 psig to about 30 psig. Inert gas and any residual carbon dioxide not utilized (such loss is kept to an absolute minimum) in the reactor is routed via a vent line to the atmosphere.

By carrying out the carbonation reaction under pressure according to this invention, the reaction rate can be increased from the rate of about 0.5 to about 1.5 grams of calcium hydroxide per liter of slurry per minute to up to about 5 to about 15 grams of calcium hydroxide per liter of slurry per minute. Thus, a production rate increase of as much as 10 fold can be achieved. This dramatic increase in reaction rate, even when employed at moderate pressures or with lower concentrations of carbon dioxide, results in a decrease in carbonation time from the prior art range of 120 to 240 minutes per batch (when conducted at atmospheric pressure conditions) to as low as 20 to 40 minutes per batch. Importantly, the carbonation reactor can be sized less than 200 gallons capacity per ton per day of PCC output, and more preferably, less than 100 gallons capacity per ton per day, and most preferably, less than 50 gallons per ton per day of PCC output.

In the process described herein, key process parameters, such as reaction temperature, carbon dioxide partial pressure, flow rate of carbon dioxide, lime slurry concentration in the carbonation reactor, agitator speed in the carbonation reactor, are effectively employed, in order to (a) increase the rate of carbonation reaction, (b) increase the carbonation efficiency, i.e., carbon dioxide utilization, and (c) to produce CaCO₃ particles of different morphology, shape, size, and size distribution.

The pressure carbonation drives the overall reaction, by improving the CO₂ mass transfer (CO₃ ⁼ formation). The higher reaction pressure evidently also increases the solubilization of Ca(OH)₂ slurry into calcium ions (Ca⁺⁺). This results in a higher reaction rate, due to increased calcium ion availability, which in turn reduces the reaction time of calcium carbonate formation.

Since much higher reaction rates are achievable, for the same production rate of PCC, this novel PCC manufacturing process can be carried out using much smaller equipment and building size than used with prior art atmospheric PCC production equipment. Overall, even considering the additional equipment required in this process, such as the higher capacity gas compressor, an overall lower capital and operating cost is achievable.

Another aspect of “pressure carbonation” is that it increases the efficiency of CO₂ utilization. One of the most significant barriers to on-site PCC facilities is the large CO₂ requirements with the conventional process. This process, however, is capable of using carbon dioxide in concentrations as low as 5 percent by volume. Because the incoming gas stream is pressurized, and the partial pressure of carbon dioxide is increased in the aqueous solution, the pressurized carbonation reaction provides higher concentrations of CO₃ ⁼ ions, since the dissolution of CO₂ is proportional to the partial pressure of CO₂. Importantly, low grade carbon dioxide containing gases (including those in the 10.0% carbon dioxide by volume range) such as are available from gas fired boilers, can be advantageously employed in on-site PCC production plants.

Even when utilizing low concentrations of CO₂ (i.e., less than about 20 percent by volume down to as low as 5 percent by volume, or lower), the utilization of the carbon dioxide may exceed 90%, and more preferably, exceed 95%, and most preferably, exceed 99%.

The pressure carbonation process for production of PCC can also produce a wide variety of crystal habits, such as scalenohedral, rhombohedral, a special “Stacked” rhombohedral, or aragonite, in different sizes, shapes, and aspect ratios.

Finally, and very importantly, the PCC provided by the instant invention produces crystals which improve key paper properties, including porosity, density, brightness, and opacity.

Calcium Silicate Hydrate (CSH)—

Detailed Description of the Process Variables

Metal Silicate Hydrates, specifically Calcium Silicate Hydrates, are generally prepared by a hydrothermal reaction between a source of alkali metal ion, in this case calcium oxide, and a source of siliceous material, preferably fluxed calcined diatomaceous earth (FCDE). Other siliceous sources may be used, including natural silica, quartz, and sodium silicate. The alkali metal ion and siliceous material are reacted under high pressure in a sealed reactor and the general chemistry of that reaction is as follows:

I. Lime Slurry Formation CaO+H₂O→Ca(OH)₂  (9) Ca(OH)₂→Ca⁺⁺+2(OH)⁻  (10) II. Silica Slurry Formation (SiO₂)_(n)+2nH₂O→nSi(OH)₄  (11) III. Hydrothermal Reaction x[Ca⁺⁺+2(OH)⁻ ]+y[Si(OH)₄]→(CaO)_(x)(SiO₂)y.(x+y)H₂O  (12)

-   -   where x=1 to 6     -    y=1 to 6

In the actual manufacturing process, the steps described below are generally taken.

Lime Slurry Formation

Lime slurry is prepared according to the slaking process previously described above, with one exception. Here, the lime slurry is not cooled. Instead, the hot lime slurry (approximately 200° F.) is screened and transferred directly to a high pressure vessel. It should be noted that the solubility of calcium hydroxide is very low in water and is inversely proportional to the temperature of that water. For example, the concentration of CaO, in pure water, at 32° F. is reported to be 0.14%. When the temperature of the water rises to boiling, 212° F., the solubility of the lime falls to 0.05%.

Siliceous Slurry Formation

Various siliceous materials such as quartz, water glass, clay, pure silica, natural silica (sand), diatomaceous earth, fluxed calcined diatomaceous earth, or any combination thereof can be used as a source of siliceous material. An ultra fine grade of fluxed calcined diatomaceous earth (FCDE) was taken and made into a slurry of ˜1.22 lbs/gallon water. An aqueous slurry of siliceous material at a concentration of from about 1 to about 1.5 pounds of silica per gallon of slurry can be used. The slurry was then preheated to near boiling. The solubility of silica/quartz, unlike that of Ca(OH)₂, is directly proportional to temperature. For example, quartz is only slightly soluble up to 212° F. From 212° F. to 266° F., it starts solubilizing, and around 518° F. (270° C.), it reaches its maximum solubility of ˜0.07%. The dissolution of silicas can be represented as per the reaction described in equation 11. The solubility of silica can be increased by raising pH and by using various additives (i.e. sodium hydroxide). In addition silica solubility is also a function of particle size, thus the reason for using ultra fine fluxed calcined diatomaceous earth (FCDE).

Hydro-Thermally Reacting the Two Slurries

First, the amount of CaO in the lime slurry and the amount of SiO₂ in the diatomaceous earth slurry were adjusted to give a predetermined CaO/SiO₂ mol ratio. Second, the concentration of the two slurries (CaO and SiO₂) and the final concentration of the mixture were adjusted so as to have a final concentration in the autoclave between 0.2 and 1.0 lbs/gallon.

The reaction itself was carried out in a pressurized vessel, with three major steps:

1) Heating the slurry to the desired temperature (e.g. 356° F. to 572° F.)

2) Reacting at temperature for a specified time (e.g. 60 min to 240 min)

3) Stopping the reaction and cooling down (e.g. 25 min to 30 min)

The autoclave was cooled down by passing quenching water through an internal cooling coil or an external jacketed cooling system. The cool down process took approximately 30-60 minutes to drop in temperature from 446° F. (230° C.) to 176° F. (80° C.), see FIG. 7.

Recognition of the inverse solubilities of lime and silica with respect to temperature and time have been utilized in an effort to produce the desired composition and various forms (mixtures) of calcium silicate hydrate material. Without limiting the invention to any theory, it can be postulated that the following reaction occurs during the hydrothermal reaction between calcious material and siliceous material.

The solid Ca(OH)₂ particles react with SiO₂ in the gel phase to give a calcium silicate hydroxide whose crystallochemical structure can be written as Ca₆Si₆O₁₇(OH)₂ (Xenotlite). As the temperature is further raised from 356° F. to 482° F., calcium silicate hydride condenses with the remaining Ca(OH)₂ particles to give yet another calcium silicate hydroxide, this time with a distinct X-ray diffraction pattern and a crystallochemical formula of Ca₄(SiO₃)₃(OH)₂ (Foshagite).

Thus, this process can produce not only single phase, but also multiple phase calcium silicate hydrates. A wide variety of silicate hydrates can be prepared by manipulating the following process parameters:

1) Lime/Silica ratio

2) Reaction Temperature

3) Slurry Concentration

4) Reaction Time

5) Heating and Cooling Sequence

By changing these variables, several different phases of calcium silicate hydroxide can be produced. Some of these phases may include:

X-ray Diffraction Peaks at 2θ Formula Morphology Major Minor Ca₄(SiO₃)₃(OH)₂ Foshagite d = 2.93 Å, d = 2.16 Å, d = 4.96 Å Ca₆Si₆O₁₇(OH)₂ Xenotlite d = 3.02 Å, d = 2.04 Å, d = 8.50 Å Ca₅Si₆O₁₇(OH)₂ Riversideite d = 3.055 Å, d = 3.58 Å, d = 2.80 Å CaCO₃ Calcite d = 3.04 Å d = 2.10 Å

The final composition may also contain minor amounts of calcite-aragonite, produced as a result of side reactions. The two main filler products provided herein include (a) varying amounts of mixtures of foshagite [Ca₄(SiO₃)₃(OH)₂] and xenotlite [Ca₆Si₆O₁₇(OH)₂] for ultra high opaque (TiSil brand calcium silicate) and (b) varying amounts of mixtures of riversidite [Ca₅Si₆O₁₇(OH)₂] and xenotolite [Ca₆Si₆O₁₇(OH)₂] for ultra high bulk (or StiSil brand calcium silicate).

X-Ray Diffraction Pattern

A unique X-ray diffraction pattern of each of the products, TiSil™ brand calcium silicate and the StiSil™ brand calcium silicate, are given below.

X-Ray Diffraction of Calcium Silicate

The crystallochemical formula of the mixture and their characteristic “d” spacing are given below: Foshagite Ca₄(SiO₃)₃(OH)₂ d = 2.97 Å, d = 2.31 Å, d = 5.05 Å (Phase I) (Major) Xenotlite Ca₆Si₆O₁₇(OH)₂ d = 3.107 Å, d = 1.75 Å, d = 3.66 Å (Phase II) (Minor)

As discussed above, precipitated calcium carbonate and calcium silicate hydrates may be prepared in common pressurized reactors. Such reactors may be designed to operate under pressures of up to as much as about 600 psig.

The above identified fillers may be further processed and/or purified in order to provide an improved paper filler product. In particular, such precipitated calcium carbonate and calcium silicate hydrate compositions may be modified, after initial manufacture, by a) in-situ, and b) post treatment, with various washing techniques or with certain chemical additives. The objective of the post manufacture in-situ and/or chemical additive treatment is to prepare specialized chemical compositions for use of such improved fillers in wood free papers (alkaline, pH>7.0) and/or wood containing papers (acidic, pH<7.0).

As discussed above, specific improved calcium carbonate, and calcium silicate hydrate based pigments are prepared in two of the following basic ways.

Precipitated Calcium Carbonate (PCC). Here lime slurry or calcium hydroxide is reacted with carbon dioxide or CO₂ containing gases in my own designed reactor system, operating under pressure. The chemical equation representing the formation of calcium hydroxide generally operates at the approximate pH range as indicated below: CaO+H₂O→Ca(OH)₂; pH=12.4  Eq. 2: Ca(OH)₂+CO₂

CaCO₃+H₂O; pH=9.4  Eq. 3:

Due to the reversible reaction equation 3, there is a certain amount of residual lime as Ca(OH)₂ which is present even after the completion of the reaction; especially if the reaction is carried out under atmospheric pressure. Also, there is also some unslaked lime which continues to leach out over a period of time. So, at any given time there is always two species, namely CaCO₃ (pH=9.4) and Ca(OH)₂ (pH=12.4). The residual lime exist in the PCC slurry.

Calcium Silicate Hydrate (Ca_(x)(SiO₃)_(y).ηH₂O). The general calcium silicate hydrate is formed under hydrothermal conditions (high pressure, ˜600 psig, and temperature, ˜250° C.) according to reactions that generally operate at the approximate pH range as indicated below: CaO+H₂O→Ca(OH)₂; pH=12.4  Eq. 9: Ca(OH)₂+SiO₂

CaSiO₃+H₂O; pH=11  Eq. 12:

Here again there is a significant amount of free lime as calcium hydroxide (Ca(OH)₂) exists in the solution phase.

The main problem is that when these alkaline pigments, pH range 8.0-11.0, are used in wood containing pulp (pH<7.0) the brightness reduces in the resulting paper due to brightness reversion by 2-6 points, as shown in FIG. 1 (Brightness Reversion Curve).

In order to provide improved, purified precipitated calcium carbonate, a method has been developed wherein the free hydroxyl ions are reduced by washing the precipitated calcium carbonate with deionized water. In another embodiment, the precipitated calcium carbonate is enhanced for near neutral pH papermaking by chemical treatment. In another embodiment enhanced filler composition are prepared by in-situ chemical treatment of the lime slurry under pressure, during the addition of CO₂ (carbonation process).

Summary of the Process for Manufacturing Precipitated Calcium Carbonate (pH>7.0) Suitable for Use in Wood Containing as Well as Wood Free Pulp, without Suppressing the pH Below 7.0.

In one embodiment, slaked lime (Ca(OH)₂) is introduced to CO₂ or CO₂ containing gases in a reactor, under pressure, which pressure ranges from about 10 psig to about 100 psig, and preferably from about 30 psig to about 70 psig. The reaction is very rapid due to high pressure accompanied by the evolution of heat. The end of reaction is indicated as the temperature reaches a maximum and the pH is reduced to ˜9.4, the equilibrium pH of calcium carbonate. The CO₂ is continued until the pH is further dropped to between 6.0 to 7.0. This reduces the amount of free lime.

There is also some calcium bicarbonate formed according to the following equation: CaCO₃+CO₂→2Ca(HCO₃)₂ pH=7.7-7.9  (13)

The free lime (hydroxyl ions) are further removed by washing with deionized water which stabilizes the pH of calcium carbonate.

In another embodiment of this invention, several chemicals can be added for in-situ co-precipitation with calcium carbonate. This will become apparent to those skilled in the art in the examples that follow.

Calcium Silicate Hydrate (Silicate Nano-Fibers or SNF)

There are no methods disclosed in the prior art to modify calcium silicate hydrate suitable for application in wood containing pulps.

The novelty of this invention is treatment of various chemicals to reduce the free lime and to render the surface of silicate nano-fibers less reactive. The process of manufacturing different phases of calcium silicate hydrate is already given before in detail.

The following portion of the specification will describe various washing steps and chemical treatment for calcium silicate hydrates (silicate nanofibers or “SNF”).

-   -   1. Silicate nano-fibers washed with carbonated deionized water.     -   2. Silicate nano-fibers treated with CO₂.     -   3. Silicate nano-fibers treated with sulphuric acid.     -   4. Silicate nano-fibers treated with oxalic acid.     -   5. Silicate nano-fibers treated with aluminum sulfate.     -   6. Silicate nano-fibers treated with polyacrylic acid and         calcium chloride.     -   7. Silicate nano-fibers treated with 2% hexametaphosphate and 2%         phosphoric acid.

Example 1 Precipitated Calcium Carbonate (pH>7.0) Formed with In-Situ Precipitation of MgO and 2.0% Sodium Hexametaphosphate and 2.0% Phosphuric Acid Followed by a DI Water Wash

Manufacturing Process:

A lime slurry of composition of 112 g/L is mixed with 5.0% by weight of magnesium oxide. CO₂ is passed through the reactor (7.0 gallon Parr reactor) under ˜50 psig pressure. Once the pH approaches 9.5-10, a mixture of sodium hexametaphosphate and phosphoric acid (2% by weight of each is added). The carbonation reaction is continued until the pH falls below 6-7. The reaction conditions are given in Table 1a. TABLE 1a Reaction conditions Description Condition Starting Lime Concentration (g/L) 112 Final Slurry Concentration (# PCC/gal) 200 CO₂ Concentration (% v/v) 100% Starting Reaction Temperature (° C.) 43 Reaction Pressure (psig) 50 Reaction Time (min) 69

This calcium carbonate slurry was filtered. The resulting cake was washed with deionized water three times. The pH of the reslurried scalenohedral precipitated calcium carbonate was recorded at ˜6.5.

Application in Wood-Containing Pulp (pH<7.0).

A mixture of 75% wood-containing and 25% Kraft was taken and mixed with 10% and 30% by weight of these washed fillers. Handsheets were made in a 8″ by 8″ Noble and Wood handsheet mold at a basis weight of 35#/3,300 ft². The sheets were tested for brightness and opacity. Another set of handsheets were made using 10% and 30% of water washed clay (pH<7.0). A third set of handsheets were made using pulp only (a mixture of 75% wood-containing and 25% Kraft; no fillers). All sheets were tested by standard TAPPI methods for TAPPI brightness and TAPPI opacity. The resulting testing data is placed in Table 1b. TABLE 1b Paper Properties 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 PCC (pH > 7.0) 71.3 94.5 80.0 94.7 Improvements PCC (pH > 7.0) over Pulp +1.9 +6.7 +10.6 +6.8 PCC (pH > 7.0) over Clay −0.8 +6.4 +6.5 +6.7

At 10% filler level, the brightness and opacity of the PCC sheet was 1.9 points and 6.7 points respectively higher over pulp only sheets.

At 30% filler the brightness and opacity of the PCC was 10.6 and 6.8 points higher than acidic pulp. Similarly, the brightness and opacity of PCC over the water washed clay was 6.5 and 6.7 points higher respectively.

At 10% filler level the brightness of the PCC sheet was ˜0.8 points lower than clay while 6.4 points higher in opacity.

Example 2 Market PCC Acid Tolerant (pH<7.0)

An acid tolerant PCC was made according to the teaching of U.S. Pat. No. 5,043,017 by adding 2% phosphoric acid and 2.0% sodium hexametaphosphate. The pH was 5.2-6.0. Handsheets were made and tested as in Example 1. The results of brightness and opacity testing are placed in Table 2a. TABLE 2a Comparison of this invention with prior art. Alkaline precipitated calcium carbonate (pH > 7.0) formed with in-situ precipitation of MgO and 2.0% sodium hexametaphosphate and 2.0% phosphuric acid AND market PCC acid-tolerant (pH < 7.0) and wood-containing pulp (pH < 7.0). 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Market PCC-AT (pH < 7.0) 72.6 92.9 79.0 92.4 PCC (pH > 7.0) 71.3 94.5 80.0 94.7 Improvements PCC (pH > 7.0) over Pulp +1.9 +6.7 +10.6 +6.8 PCC (pH > 7.0) over Market −1.3 +1.6 +1.0 +2.2 PCC-AT (pH < 7.0)

The data at 10% filler indicates that, while the brightness of the sheet made using PCC (pH>7.0) according to this invention was lower by 1.3 points, the opacity was 1.6 points better. However, at 30% filler level both brightness and opacity of PCC was 1.0 and 2.2 points higher than market PCC-AT (acid tolerant). It is clear that 1) PCC of this invention is compatible with wood containing acidic pulp. 2) The PCC of this invention gives better opacity than acid tolerant PCC of prior art.

Example 3 Precipitated Calcium Carbonate (pH>7.0) Formed with In-Situ Treatment of Sodium Silicate Followed by a Post Treatment DI Water Wash

Scalenohedral PCC was prepared in the lab by following the same procedure as in Example 1. However, sodium silicate (5% by weight) was added for in-situ co precipitation during the pressurized carbonation process. The PCC was washed with deionized water. Handsheets were also made at 10% and 30% filler levels and tested as in Example 1. The results are placed in Table 3a. TABLE 3a Paper Properties 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 PCC (pH > 7.0) 70.5 94.3 75.9 94.6 Improvements PCC (pH > 7.0) over Pulp +1.1 +6.5 +6.5 +6.8 PCC (pH > 7.0) over Clay −1.6 +6.2 +2.4 +6.7

Example 4 Precipitated Calcium Carbonate (pH>7.0) Formed with Insitu Precipitation of 2.0% Sodium Hexametaphosphate and 2.0% Phosphuric Acid

The scalenohedral PCC was prepared according to the same procedure as in Example 1, except a mixture of sodium hexametaphosphate and phosphoric acid was added to the lime slurry for in-situ co precipitation of PCC during the pressurized carbonation process. The resulting PCC was washed with deionized water. This PCC was used, as in Example 1, to make 10% and 30% filled handsheets. These sheets were tested for brightness and opacity. Results are given in Table 4a. TABLE 4a Paper Properties 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 PCC (pH > 7.0) 68.3 93.7 74.7 96.5 Improvements PCC (pH > 7.0) over Pulp −1.1 +5.9 +5.3 +8.7 PCC (pH > 7.0) over Clay −3.8 +5.6 +1.2 +8.6

Example 5 DI Water-Washed Aragonite Precipitated Calcium Carbonate (Alkaline, pH>7.0)

An aragonite PCC was prepared in the lab using pressurized carbonation conditions given in Table 5a. TABLE 5a Process conditions Description Condition Starting Lime Concentration (g/L) 128 Final Slurry Concentration (# 229 PCC/gal) CO₂ Concentration (% v/v) 25% Starting Reaction Temperature (° C.) 60 Reaction Pressure (psig) 70 Reaction Time (min) 65

An aragonite seed (Mississippi Lime M-60) was used to promote aragonite crystal formation. The PCC was washed with DI water. The handsheets were made at 10% and 30% filler and tested as in Example 1. The results of the testing are given in Table 5b. TABLE 5b Paper Properties. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 PCC (pH > 7.0) 69.9 93.2 74.3 93.9 Improvements PCC (pH > 7.0) over Pulp +0.5 +5.4 +4.9 +6.1 PCC (pH > 7.0) over Clay −2.2 +5.1 +0.8 +6.0

The pH stability of the aragonite crystal formed by pressure carbonation and deionized water washing is given in FIG. 2. As shown in the curve the pH of PCC of this invention was fairly stable at (˜7.8) for a period over 1400 minutes (˜24 hours).

Example 6 Scalenohedral PCC Precipitated Calcium Carbonate (pH>7.0)

The precipitated calcium carbonate was prepared according to the process condition given in Table 6a. TABLE 6a Process conditions. Description Condition Starting Lime Concentration (g/L) 112 Final Slurry Concentration (# 200 PCC/gal) CO₂ Concentration (% v/v) 100% Starting Reaction Temperature (° C.) 43 Reaction Pressure (psig) 50 Reaction Time (min) 69

The resulting PCC was washed with deionized water 3 times. The pH of the scalenohedral PCC reached equilibrium at ˜pH 7.8 to 8.0 as shown in FIG. 3. The handsheets were made and tested at 10% and 30% filler levels as in Example 1. The results from the handsheet comparison are in Table 6b. TABLE 6b Paper Properties 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 PCC (pH > 7.0) 69.9 93.2 74.3 93.9 Improvements PCC (pH > 7.0) over Pulp +0.5 +5.4 +4.9 +6.1 PCC (pH > 7.0) over Clay −2.2 +5.1 +0.8 +6.0

Example 7 DI Water Washed Rhombohedral Precipitated Calcium Carbonate (pH>7.0)

A rhombohedral PCC was prepared using the same equipment as in Example 1. The process conditions are given in Table 7a. The resulting PCC was washed with deionized water 3 times to remove any free lime. TABLE 7a Manufacturing conditions for alkaline rhombohedral SPCC (pH > 7.0). Description Condition Starting Lime Concentration (g/L) 50 Final Slurry Concentration (# 90 PCC/gal) CO₂ Concentration (% v/v) 100% Starting Reaction Temperature (° C.) 15 Reaction Pressure (psig) 70 Reaction Time (min) 11

The pH of the PCC reached equilibrium at pH 6.8. The pH removed stable for a period of 24 hours as shown in FIG. 4.

Example 8 Precipitated Calcium Carbonate (pH>7.0) Formed with Treatment of Sodium Polyacrylate and Calcium Chloride

Aragonite PCC produced in Example 5 was water washed with DI water 3 times. The resulting PCC was treated with sodium polyacrylate, (Colloid 211, Kemira Chemicals, Georgia, USA) at 1.0% by weight. The well dispersed slurry was than kneaded with 1.7% 1 molar calcium chloride. The pH stability curve is given in FIG. 5.

Handsheets were made and tested by following the same procedures as in Example 1. The results are given in Table 8a. TABLE 8a Precipitated calcium carbonate (pH > 7.0) formed with in-situ treatment of sodium polyacrylate and calcium chloride AND acidic water- washed clay (pH < 7.0) and wood-containing pulp (pH < 7.0). 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 PCC (pH > 7.0) 69.8 92.9 75.3 94.4 Improvements PCC (pH > 7.0) over Pulp +0.4 +5.1 +5.9 +6.6 PCC (pH > 7.0) over Clay −2.3 +4.8 +1.8 +6.4

Example 9 Manufacturing of Calcium Silicate Hydrate:Silicate Nano-Fibers(SNF)

Silicate Nano-Fibers were prepared in the lab (Parr reactor, 5 gallon) according to the process conditions given in Table 9a. TABLE 9a Process conditions. Description Condition Lime to Silica Molar Ratio (unitless) 1.30 Slurry Concentration (#/gal) 0.40 Bulk Reaction Temperature (° C.) 255 Bulk Reaction Time (hours) 2.0

The hydrothermally produced silicate nano-fibers were washed by carbonated deionized water 3 times.

Handsheets were made following the same procedure as in Example 1. However, in addition to comparing SNF with water washed clay, handsheets were also made using water washed clay (WWP) and calcined clay blend (pH 6.8). The results of brightness and opacity testing for unfilled sheets (pulp only pH<7.0) clay filled sheets, SNF filled sheets, and clay and water washed clay blend sheets at 10% and 30% filler level are given in Tables 9b and 9c. TABLE 9b Paper properties comparison of SNF with clay. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 Silicate Nano-Fiber 72.2 92.9 77.9 95.1 (Alkaline, pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +2.8 +5.1 +8.5 +7.3 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, +0.2 +4.8 +4.4 +7.1 pH > 7.0) over Clay

TABLE 9c Paper properties comparison of SNF with calcined clay blends. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay Blend 74.1 88.7 77.1 89.5 Silicate Nano-Fiber 72.2 92.9 77.9 95.1 (Alkaline, pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +2.8 +5.1 +8.5 +7.3 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, −1.9 +4.2 +0.8 +5.6 pH > 7.0) over Clay Blend

Both at 10 and 30% SNF levels both sheet brightness and opacities were significantly better than pulp. Similarly comparing SNF with calcine blends of clay, the sheet brightness was 1.9 points lower, but the sheet opacity was 4.2 points higher at 10% filler level.

At 30% filler level the SNF sheet had 0.8 points higher brightness and 5.6 points higher opacity. This indicates that silicate nano-fibers that are produced by hydro-thermal process are also compatible with wood containing pulp without any significant loss in brightness, while significantly improving opacity.

Example 10 Silicate Nano-Fibers (SNF, Alkaline, pH>7.0); Treated with CO2

Silicate nano-fibers were prepared following the procedure in Example 9. The SNF was further treated with CO₂ to pH 6.8. The pH stability for short term and long term are given in FIGS. 6 and 7.

Handsheets were made using SNF, clay, and clay plus calcined clay blends. These sheets were tested by TAPPI methods for brightness and opacity as in Example 1. The results are placed in Tables 10a and 10b TABLE 10a Paper properties comparison of SNF + CO₂ with clay. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 Silicate Nano-Fiber 72.1 92.5 77.9 95.3 (Alkaline, pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +2.7 +4.7 +8.5 +7.5 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, +0.0 +4.4 +4.4 +7.4 pH > 7.0) over Clay

TABLE 10b Paper properties comparison of SNF + CO₂ with calcined clay blends. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay Blend 74.1 88.7 77.1 89.5 Silicate Nano-Fiber 72.1 92.5 77.9 95.3 (Alkaline, pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +2.7 +4.7 +8.5 +7.5 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, −2.1 +3.9 +0.8 +5.9 pH > 7.0) over Clay Blend

Example 11 Silicate Nano-Fibers Treated with Sulfuric Acid

Silicate nano-fibers (SNF) prepared in Example 9 were further treated with sulfuric acid (2.0% on dry pigment). The stability curves for long and short term are given in FIG. 8 and FIG. 9.

Handsheets were made and tested, using 10% and 30% SNF, water washed clay and water washed and calcined clay blends as in Example 1. The results are given in Table 11a and 11b. TABLE 11a Paper properties comparison of SNF + sulfuric acid with clay. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 Silicate Nano-Fiber 72.4 92.7 78.7 95.5 (Alkaline, pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +3.0 +4.9 +9.3 +7.7 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, +0.3 +4.6 +5.2 +7.5 pH > 7.0) over Clay

TABLE 11b Paper properties comparison of SNF + sulfuric acid with calcined clay blends. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay Blend 74.1 88.7 77.1 89.5 Silicate Nano-Fiber 72.4 92.7 78.7 95.5 (Alkaline, pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +3.0 +4.9 +9.3 +7.7 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, −1.7 +4.1 +1.6 +6.0 pH > 7.0) over Clay Blend

Example 12 Silicate Nano-Fibers Treated with Oxalic Acid

Here the silicate nano-fibers are prepared as in Example 9 where further treated with oxalic acid. The pH stability curve for short and long terms are given in FIG. 10 and FIG. 11. Handsheets were made and tested at 10% and 30% filler level following the same procedure as in Example 1.

The results of brightness and opacity testing of the handsheets are given in Table 12a and 12b. TABLE 12a Paper properties comparison of SNF + oxalic acid with clay. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 Silicate Nano-Fiber (Alkaline, 72.6 93.0 79.7 95.1 pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +3.2 +5.2 +10.3 +7.3 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, +0.5 +4.9 +6.2 +7.2 pH > 7.0) over Clay

TABLE 12b Paper properties comparison of SNF + oxalic acid with calcined clay blends. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay Blend 74.1 88.7 77.1 89.5 Silicate Nano-Fiber 72.6 93.0 79.7 95.1 (Alkaline, pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +3.2 +5.2 +10.3 +7.3 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, −1.6 +4.3 +2.6 +5.7 pH > 7.0) over Clay Blend

Example 13 Silicate Nano-Fibers Treated with Aluminum Sulfate

Silicate nano-fibers as prepared in Example 9 were further treated with aluminum sulfate. The short and long term pH stability curves are given in FIG. 12 and FIG. 13.

Handsheets were made and tested at 10% and 30% filler level using SNF, water washed clay and water washed clay and calcined clay blends.

The results of testing the brightness and opacity are given in Table 13a and 13b. TABLE 13a Paper properties comparison of SNF + alum with clay. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 Silicate Nano-Fiber (Alkaline, 72.1 92.6 77.6 95.4 pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +2.7 +4.8 +8.1 +7.6 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, −0.0 +4.5 +4.0 +7.5 pH > 7.0) over Clay

TABLE 13b Paper properties comparison of SNF + alum with calcined clay blends. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay Blend 74.1 88.7 77.1 89.5 Silicate Nano-Fiber (Alkaline, 72.1 92.6 77.6 95.4 pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +2.7 +4.8 +8.1 +7.6 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, −2.1 +3.9 +0.5 +6.0 pH > 7.0) over Clay Blend

Example 14 Silicate Nano-Fibers Treated with Polyacrylic Acid (Colloid 211) and Calcium Chloride

The silicate nano-fibers (SNF) prepared in Example 9 were further treated with polyacrylic acid. The fully dispersed slurry of SNF was further treated with calcium chloride.

The short and long term stability curves of SNF are given in FIG. 14 and FIG. 15.

Handsheets were made and tested following the same procedure as in Example 1. The results of the handsheet testing for brightness and opacity are given in Table 14a and Table 14b. TABLE 14a Paper properties comparison of SNF + polyacrylic acid and calcium chloride with clay. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 Silicate Nano-Fiber (Alkaline, 73.4 93.7 78.9 96.2 pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +4.0 +5.8 +9.5 +8.4 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, +1.3 +5.6 +5.4 +8.3 pH > 7.0) over Clay

TABLE 14b Paper properties comparison of SNF + polyacrylic acid and calcium chloride with calcined clay blends. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay Blend 74.1 88.7 77.1 89.5 Silicate Nano-Fiber (Alkaline, 73.4 93.7 78.9 96.2 pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +4.0 +5.8 +9.5 +8.4 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, −0.8 +5.0 +1.9 +6.8 pH > 7.0) over Clay Blend

Example 15 Silicate Nano-Fibers Treated with a Mixture of Sodium Hexametaphosphate and Phosphuric Acid

The silicate nano-fibers prepared as in Example 9 were further treated with a mixture of sodium hexametaphosphate and phosphoric acid (2.0% by weight on dry pigment for each). The pH stability curves for the short and long term are given in FIG. 16 and FIG. 17.

The handsheets were made and tested for 10% and 30% filler in the procedure in Example 1. The results of the brightness and opacity testing are given in Table 15a and Table 15b. TABLE 15a Paper properties comparison of SNF + 2% sodium hexametaphosphate and 2% phosphoric acid with clay. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay 72.1 88.1 73.5 87.9 Silicate Nano-Fiber (Alkaline, 74.2 93.5 80.0 95.9 pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +4.8 +5.6 +10.6 +8.0 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, +2.1 +5.4 +6.5 +7.9 pH > 7.0) over Clay

TABLE 15b Paper properties comparison of SNF + 2% sodium hexametaphosphate and 2% phosphoric acid with calcined clay blends. 10% Filler 30% Filler Brightness Opacity Brightness Opacity Conditions Pulp 69.4 87.8 69.4 87.8 Clay Blend 74.1 88.7 77.1 89.5 Silicate Nano-Fiber (Alkaline, 74.2 93.5 80.0 95.9 pH > 7.0) Improvements Silicate Nano-Fiber (Alkaline, +4.8 +5.6 +10.6 +8.0 pH > 7.0) over Pulp Silicate Nano-Fiber (Alkaline, +0.1 +4.8 +2.9 +6.4 pH > 7.0) over Clay Blend

The crystalline microfibers as described herein have advantageous properties when utilized as a paper filler, particularly in uncoated groundwood, and in coated groundwood, in uncoated fine paper, and in coated fine paper. The aforementioned adsorptive properties help to adsorb printing ink in the papers. Also, it helps the paper sheet itself to absorb fines, so that it improves overall sheet retention during the papermaking process. Overall, final paper products exhibit improved porosity, improved smoothness, improved bulk, and improved stiffness. Also, brightness and opacity are maintained or improved. Moreover, the printability of the final product is significantly improved, due to the improved ink adsorption.

It is to be appreciated that the herein described unique, light, fluffy adsorptive calcium silicate hydrate products, and the method of producing the same, and the paper products produced using such products, each represent an appreciable improvement in the field of manufacture of paper.

The improved precipitated calcium carbonate manufacturing process and the novel calcium silicate hydrate manufacturing process, control of the pH, temperature, and time of reaction is determined by the nature of the progress of the reaction in a particular batch. Importantly, the process is readily automated and can be put into an automated process control environment. Although numerous examples have been provided in detail, it will be readily apparent to those skilled in the art that this unique pressurized production process for manufacture of calcium carbonate, and of the manufacture of calcium silicate in common equipment, and the apparatus for implementing such a process, may be modified from those embodiments provided herein, without materially departing from the novel teachings and advantages provided.

It will thus be seen that the objects set forth above, including those made apparent from the preceding description, are efficiently attained. Since certain changes may be made in carrying out the method for production of precipitated calcium carbonate and of calcium silicate, according to the teachings herein, it is to be understood that this invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Many other embodiments are also feasible to attain advantageous results utilizing the principles disclosed herein. Therefore, it will be understood that the foregoing description of representative embodiments of the invention have been presented only for purposes of illustration and for providing an understanding of the invention, and it is not intended to be exhaustive or restrictive, or to limit the invention only to the precise forms disclosed.

The intention is to cover all modifications, equivalents, and alternatives falling within the scope and spirit of the invention, as expressed herein above and in the appended claims. As such, the claims are intended to cover the methods, apparatus, structures (including crystal structures), and products described herein, and not only the equivalent methods or structural equivalents thereof, but also equivalent methods or structures. The scope of the invention, as described herein and as indicated by the appended claims, is thus intended to include variations from the embodiments provided which are nevertheless described by the broad meaning and range properly afforded to the language of the claims, as explained by and in light of the terms included herein, or the legal equivalents thereof. 

1. A method for the production of calcium carbonate, said method comprising: (a) providing an aqueous lime slurry, said aqueous lime slurry comprising (i) Ca(OH)₂ solids and (ii) dissolved Ca(OH)₂ in the form of Ca⁺⁺ ions; (b) screening grit from said aqueous lime slurry; (c) conditioning said aqueous lime slurry to a predetermined temperature; (d) feeding a first portion of said aqueous lime slurry into a first reactor; (e) agitating the contents of said first reactor at super-atmospheric pressure; (f) introducing a stream of CO₂ into said aqueous lime slurry in said first reactor, to form CO₃ ⁻²; (g) reacting said CO₃ ⁻²; and said Ca⁺⁺ in a carbonation reaction to produce insoluble precipitated calcium carbonate (CaCO₃) in said first reactor; (h) removing said insoluble precipitated calcium carbonate and associated water from said first reactor; (i) dewatering said insoluble precipitated calcium carbonate; (j) washing said insoluble precipitated calcium carbonate with a selected wash water;
 2. The method as set forth in claim 1, wherein said selected wash water comprises high purity water.
 3. The method as set forth in claim 2, wherein said high purity water comprises deionized water.
 4. The method as set forth in claim 1, further comprising adding a sodium silicate solution to said reactor, so that said sodium silicate is present during the production of insoluble precipitated calcium carbonate.
 5. The method as set forth in claim 4, wherein said sodium silicate is added in the form of an aqueous sodium silicate stream at about 5% sodium silicate.
 6. The method as set forth in claim 1, further comprising adding (a) magnesium oxide, (b) a selected hexamataphosphate, and (c) phosphoric acid to said reactor, so that said additives are present during the production of insoluble precipitated calcium carbonate.
 7. The method as set forth in claim 6, wherein said phosphoric acid comprises about a 2% phosphoric acid aqueous mixture.
 8. The method as set forth in claim 1, wherein said insoluble precipitated calcium carbonate comprises aragonite.
 9. A method for the production of calcium silicate hydrate, said method comprising: (a) charging a reactor with a first aqueous silica slurry comprising silica at a concentration of from about 1 to about 1.5 pounds of silica per gallon of said first aqueous silica slurry; (b) charging said reactor with an aqueous lime slurry; (c) heating the contents of the reactor under hydrothermal conditions to produce a calcium silicate. (d) removing the calcium silicate from the reactor; (e) dewatering said calcium silicate; (f) washing said calcium silicate with a selected wash water;
 10. The method as set forth in claim 9, wherein said selected wash water comprises high purity water.
 11. The method as set forth in claim 10, wherein said high purity water comprises deionized water.
 12. The method as set forth in claim 9, wherein the properties of the calcium silicate hydrate product are controlled by adjusting one or more of the process variables selected from a group consisting of: (1) calcium to silica mole ratio, (2) lime plus silica slurry concentration, (3) reaction temperature, and (4) reaction pressure.
 13. The method as set forth in claim 12, wherein the calcium to silica mole ratio is in the range of 1.2 to 1.6.
 14. The method as set forth in claim 13, wherein said calcium silicate hydrate comprises foshagite consisting of fibrous crystals ranging in size from 0.1 to 0.3 microns and in length up to about 5 microns.
 15. The method as set forth in claim 12, wherein said calcium silicate hydrate comprises primary fibrous particles interlocked into a secondary particle structure, and wherein said secondary particle structure has a size varying from about 10 microns to about 40 microns.
 16. The method as set forth in claim 40 wherein the x-ray diffraction pattern of said calcium silicate hydrate, when dried, comprises: Foshagite: dMajor=2.97 Å  dMinor=5.05 Å Xenotlite: dMajor=3.107 Å  dMinor=3.66 Å
 17. A paper composition, said composition comprising: an effective amount of a filler, said filler comprising a multiple phase calcium silicate hydrate comprising foshagite and xonotlite, and having peaks in the XRD patterns from the foshagite and xenotlite components in the complex having the characteristic XDR, which comprises: Foshagite: dMajor=2.97 Å  dMinor=5.05 Å Xenotlite: dMajor=3.107 Å  dMinor=3.66 Å
 18. A paper composition according to claim 17, wherein said multiple phase calcium silicate hydrate has a water absorption range of at least about 500 percent.
 19. A paper composition according to claim 17, wherein said multiple phase calcium silicate hydrate has a water adsorption range of up to approximately 1000 percent.
 20. A paper composition according to claim 17, wherein said paper is a wood containing paper.
 21. A paper composition according to claim 17, wherein said filler comprises at least 30% of said paper by weight.
 22. A paper composition according to claim 21, wherein brightness of said paper is at least 74 GE.
 23. A paper composition according to claim 21, wherein opacity of said paper is at least
 94. 24. A paper composition according to claim 21, wherein opacity of said paper is at least
 95. 25. A paper composition according to claim 21, wherein opacity of said paper is at least
 96. 26. A method for the hydrothermal production of calcium silicate hydrate and calcium carbonate in a set of common reactors, said method comprising: (a) providing an aqueous lime slurry, said aqueous lime slurry comprising (i) Ca(OH)₂ solids and (ii) dissolved Ca(OH)₂ in the form of Ca⁺⁺ ions; (b) screening grit from said aqueous lime slurry; (c) conditioning said aqueous lime slurry to a predetermined temperature; (d) feeding a first portion of said aqueous lime slurry into a first reactor of said set of common reactors; (e) agitating the contents of said first reactor at super-atmospheric pressure; (f) introducing a stream of CO₂ into said aqueous lime slurry in said first reactor, to form CO₃ ⁻²; (g) reacting said CO₃ ⁻²; and said Ca⁺⁺ in a carbonation reaction to produce insoluble precipitated calcium carbonate (CaCO₃) in said first reactor; (h) removing said insoluble precipitated calcium carbonate and associated water from said first reactor; (i) dewatering said insoluble precipitated calcium carbonate; (j) washing said insoluble precipitated calcium carbonate with a selected wash water; (k) charging a second reactor of said set of common reactors with a first aqueous silica slurry comprising silica at a concentration of from about 1 to about 1.5 pounds of silica per gallon of said first aqueous silica slurry; (l) charging said second reactor of said set of common reactors with a second portion of said aqueous lime slurry; (m) heating the contents of said second reactor under hydrothermal conditions to produce a calcium silicate. (n) removing said calcium silicate from said second reactor; (o) dewatering said calcium silicate; (p) washing said calcium silicate with a selected wash water; (q) switching feed of said first portion of said aqueous lime slurry and said CO₂ to said second reactor from said first reactor, and switching feed of said first aqueous silica slurry and said second portion of aqueous lime slurry to said first reactor, so that precipitated calcium carbonate is produced in said second reactor, and calcium silicate is produced in said first reactor.
 27. The method as set forth in claim 26, wherein said silica comprises fluxed calcined diatomaceous earth (FCDE).
 28. The method as set forth in claim 26, wherein said selected wash water comprises high purity water.
 29. The method as set forth in claim 28, wherein said high purity water comprises deionized water.
 30. The method as set forth in claim 26, further comprising adding, during production of said precipitated calcium carbonate, (a) magnesium oxide, (b) a selected hexamataphosphate, and (c) phosphoric acid to said reactor, so that said additives are present during the production of insoluble precipitated calcium carbonate. 